A. Field of the Invention
The present invention refers to a glass composition for the commercial production of a neutral gray glass mainly for use in the automotive industry such as windshields and front sidelights, having an illuminant “A” light transmission (TLA) greater of 65%, a total solar energy transmittance (TS) of less than or equal to 60%, and a solar ultraviolet transmittance (TUV) of less than 46%; a dominant wavelength from 490 nm to 600; and excitation purity of less than 6.
B. Description of the Related Art
Several patents have been developed for obtaining gray glass, for “automotive” purposes, having a light transmission greater to 70, which meets with the requirements of the U.S. Federal Motor Vehicle Safety Standard. For the construction industry there is not restriction and smaller values can be obtained as well as thicknesses between 1.6 and 12 mm.
The glasses disclosed in almost all the prior patents referring to a type of neutral gray glass for automotive purposes, are based on three basic components: iron oxide, cobalt oxide and selenium. These components are additionally combined with Nickel Oxide or Manganese Oxide commonly called Manganese Dioxide using different proportions and, together with the typical formulation of a soda-lime-silica glass, constitutes the basic composition of the glass.
That is the case of the glasses of the U.S. Pat. No. 7,071,133 of Arbab, et al, issued on Jul. 4, 2006, which has glass redox value from 0.2 to 0.675; the U.S. Pat. No. 6,821,918 of Boulos, et al, issued on Nov. 23, 2004 in which iron oxide, cobalt oxide selenium and manganese are used as main components. The manganese compound is present in an amount of 0.1 to 0.5 wt. % based on MnO2 in the glass composition. The presence of manganese substantially prevents the formation of the amber color. This manganese compound can be added to the batch glass components in a variety forms, e.g., but not limited to MnO2, Mn3O4, MnO, MnCO3, MnSO4, MnF2, MnCl2, etc.
Some other glasses disclosed in other patents, such as those mentioned in the following paragraphs use, besides the three mentioned components, different metallic elements conferring the characteristics to the final product, that allow them a TLA>70%, in order to be used in the construction and automotive industries.
That is the case of the glasses of the U.S. Pat. No. 6,114,264 of Krumwiede, et al issued on Sep. 5, 2000, wherein the color of the glass is characterized by dominant wavelengths in the range of 480 to 555 nanometers, an excitation purity of no higher than 8 percent and a luminous transmittance of 70 percent or greater at a thickness of 3.9 millimeters; the U.S. Pat. No. 6,998,362 of Higby, et al issued on Feb. 14, 2006, wherein the color of the glass is characterized by a dominant wavelength less than 560 nanometers, a color purity of no higher than 6 percent and a visible light transmission of 70 percent or greater at a thickness of 4 millimeters, and wherein the percent reduction of the total iron is between 21% and 34%; the U.S. Pat. No. 7,179,763 of Teyssedre, et al, issued Feb. 20, 2007, the glass having an overall light transmission under illuminant A greater than 67 for a glass thickness equal to 3.85 mm; and, the U.S. Pat. No. 5,958,811 of Sakaguchi, et al issued on Sep. 28, 1999, wherein an ultraviolet and infrared radiation absorbing glass composition has a visible light transmission of 70% or more as measured with the CIE standard illuminant A, when said glass has a thickness of 3.25 to 6.25 mm. The glass composition includes CoO, Se and Fe2O3 as main components, as well as, rare earths CeO2 and La2O3.
The U.S. Pat. No. 6,235,666 (Cochran, et al), U.S. Pat. No. 6,403,509 (Cochran, et al), U.S. Pat. No. 6,498,118 (Landa, et al), U.S. Pat. No. 6,573,207 (Landa, et al), U.S. Pat. No. 6,521,558 (Landa, et al), U.S. Pat. No. 6,716,780 (Landa, et al), U.S. Pat. No. 7,135,425 (Thomsen, et al) and U.S. Pat. No. 7,151,065 (Thomsen, et al) are related with glasses with a luminous transmittance greater of 70 percent. Their main colorants are CoO, Se, y Fe2O3. The Se and CoO can be partially or totally substituted by a combination of rare earths such as Er2O3, Y2O3, Ho2O3, CeO2. However, a disadvantage on the use of rare earth oxides in the glass compositions are the high costs.
Additionally, the U.S. Pat. No. 5,308,805 of Baker et al, issued May 4, 1994, describes a neutral gray glass having a low transmission, in which one of the claimed components is the nickel oxide in proportions of 100 to 500 ppm.
In the past, the heat absorbing gray glasses containing nickel in their structure, frequently presented inclusions of nickel in the form of sulfide which, during the melting of the glass were formed until appearing as small invisible particles which were impossible to distinguish in viewing an already formed glass. These inclusions of nickel sulfide are due to their high coefficient of thermal expansion that can cause thermal stresses sufficient to fracture a glass plate. This is a singular problem when the glass pieces are subjected to a thermal treatment as the tempering, in which the presence of the nickel sulfide causes an excessive percentage of breakdown pieces during or as a consequence of the tempering process.
An additional disadvantage of the glasses containing nickel is the change of color that they undergo after the thermal process, such as for example, after tempering.
U.S. Pat. No. 5,023,210 of Krumwide et al, issued Jun. 11, 1991, discloses a low transmission (the glass having a luminous transmittance less than 20 percent) neutral gray glass composition that does not includes nickel. In order to achieve similar characteristics to that of a neutral gray glass, Krumwide uses chromium oxide in amounts of 220 to 500 ppm as Cr2O3, in its composition which, in these proportions, produces a gray tone and adjusts the levels of selenium and cobalt oxide in order to make it a neutral tone. However, in previous references it is mentioned a preference of not using these compounds because of the problems presented by the difficulty of melting the chromium compounds (U.S. Pat. No. 4,837,206), and additionally because these have difficulties in order to discard the solid materials containing said compounds. Also, in the U.S. Pat. No. 5,308,805, there is mentioned the inconvenience of the chromium oxide used like coloring agent, since it requires the use of additional operations and apparatuses to the conventional ones into the melting furnaces in order to reach the necessary conditions to produce the desired glasses.
The U.S. Pat. No. 5,346,867 of Jones et al, issued Sep. 13, 1994, discloses a heat absorbing glass composition having a neutral gray color, which uses manganese and titanium oxide in order to increase the retention of the selenium (that is a high cost component), during the production process. The neutral gray glass having a 4 mm control thickness, a light transmittance using illuminant A of 10.0% to 55.0%. Although of previous references (U.S. Pat. No. 4,873,206), it was known that the use of the manganese has a tendency to form a yellowish-brown coloration when it is exposed to the ultraviolet radiation making it difficult to maintain the uniformity of the product, and the use of the titanium causes a yellowish coloration when the glass enters in contact with the liquid tin of the float process. This is what makes undesirable these two aspects during the production of the glass because it makes critical the control of color in order to obtain the desired tone during the manufacture. Jones et al mentioned in their patent '867, that the process of solarization is a phenomenon associated with the change of Fe3+ to Fe2+ which cause an undesirable change in the color, mentioning that they found that this does not occur in the disclosed glass and additionally the use of the titanium oxide is incorporated into the glass in order to obtain the desired range of dominant wave length, as well to reduce the transmission of ultraviolet radiation.
On the other hand, it is well known by the persons skilled in the art, that the addition or substitution of one or more colorants for other colorants, or the change in the relative proportional amount in the glass composition, affects not only the color of the product, as for example the dominant wave length of the color or the excitation purity, but also the luminous transmission, the heat absorption and additional properties such as the transmission of ultraviolet and infrared radiation.
It has been known that copper played an important role in the production of colored glass, ceramics and pigments. It has been recognized, for example, the coloration of the Persian ceramic for their tonality conferred by the copper. Of special interest for ceramic artists are the turquoise blue and especially the Egyptian and Persian blue dark (Woldemar A. Weil; Colored Glasses, Society of Glass Technology, Great Britain, p. 154-167, 1976).
Copper has been used in the glass compositions, not only in those of soda-lime-silica type, but also in others such as those containing, for example, borosilicate. Therefore, the developed color depends on the base of the glass, on its concentration and on its oxidation state.
For the case of the above mentioned glass as a base, the copper in the form of the oxide imparts a blue coloration of a greenish tone, specifically turquoise, however in the glass, the copper can be in its monovalent state, which does not impart color. So, the blue greenish coloration depends not only on the amount of copper present, but on the ionic balance between the cuprous and cupric states. The maximum absorption of the copper oxide is in a band centered at 780 nm and a maximum weak secondary peak is present at the 450 nm, which disappears at high soda content (around 40% weight). (C. R. Bamford, Colour Generation and Control in Glass, Glass Science and Technology, Elsevier Scientific Publishing Company, p. 48-50, Amsterdam, 1977).
In the production of red ruby glass, a mixture containing copper oxide together with any reducer agent (SnO is commonly used), is melted in reduced conditions. The initial mixture shows the blue characteristic color of the copper II, but as soon as the melting begins, changes the color to a pale straw yellow which takes place during this stage. Due to a thermal treatment to a temperature between the annealing point and the softening point, the ruby red color is developed. If, during the melt, the reduction state is carried out beyond a critical stage, the color changes to brown and appears opaque or “turned off”. On the other hand, if the copper is insufficiently reduced, some traces of blue color are kept and the ruby red color is not developed (Amal Paul, Chemistry of Glasses, Chapman and Hall, p. 264-270, London, 1982).
U.S. Pat. No. 2,922,720 of Parks et al, issued Jun. 20, 1957, discloses the use of the copper in the glass as: “ . . . The copper has been used as coloring agent for glass upon developing a coloration ruby red, but in order to obtain the color in a open melt furnace, it has been necessary the use of cyanogens as reducer agent . . . ”, additionally mentions the effect of the copper in the coloration of the glass, as due to the colloidal suspension of particles of metallic copper in the glass, and by analogy it is believed that a particle size produces the ruby red colors, depending on the intensity of the color of the copper concentration. For smaller particle sizes, the effect of color is null.
In the present application, the incorporation of cupper oxide (CuO), in combination with the iron oxide, cobalt oxide and selenium is used as an alternative for obtaining a gray tonality with a light transmission>70% for use in the automotive industry. This avoids the intentional addition of some colorants as the nickel, manganese, TiO2 or a combination of rare earths.
Furthermore, the Cobalt Oxide (expressed as Co3O4) is partially substituted by Copper Oxide (CuO) and in some examples is avoided. This substitution is possible because the CuO and the Co3O4 provides a blue tonality to the glass.% Redox or % ferrous=% FeO (express as Fe2O3)/(% total Fe2O3)
The neutral tonality is obtained with the combination of iron oxide (Fe2O3), which causes a change of color of the glass from a yellow to yellow-green (lower redox) to a blue (higher redox), depending on the % of reduction. If redox is higher, it is possible to avoid cobalt oxide (blue) and add only selenium (coloration from pink to red-brown) and copper oxide (turquoise-blue). On the other hand, if redox is lower it is necessary a combination of Copper oxide-cobalt oxide. In the last combination, Cobalt is partially substituted by Copper.
Additionally, also is provided a reduction in the ultraviolet radiation transmission and a reduction in the near infrared region for the bands of absorption around the 800 nanometers which help to reduce the infrared solar transmission.
It has been verified that for industrial production is feasible to add CuO, in minor concentrations to 120 ppm for a glass thickness of 4.0 mm and less than 100 ppm for a glass thickness of 6.0 mm.
The glass also can be manufactured with a thickness from about 1.6 millimeters to about 12 mm. If higher concentrations of CuO are presented within of the float chamber, a reduction process in the atmosphere could be given, presenting a red coloration on the glass surface. This effect related with the residence time and to the advancing velocity of the glass ribbon can be intense and observable on the glass surface.
So that, in the present invention, a gray neutral glass composition has an illuminant “A” light transmission (TLA) greater of 70%, a total solar energy transmittance (TS) of less than or equal to 60%, and a solar ultraviolet transmittance (TUV) of less than 46%, is achieved.